Feat/add optional header support to seeds

[aammett]

Resolves #11334

Problem

If I've configured my seed's column names in a yml file, I don't want to also keep a header row up-to-date in my csv seed file.

seeds:
  - name: my_seed
    columns:
      - name: country_code
        data_type: varchar(2)
      - name: country_name
        data_type: varchar(32)

country_code,country_name
US,United States
CA,Canada
GB,United Kingdom

Instead, I should be able to configure my seed to not need a header row if I've configured my column names in yml already.

seeds:
  - name: my_seed
    config:
      header: false
    columns:
      - name: country_code
        data_type: varchar(2)
      - name: country_name
        data_type: varchar(32)

US,United States
CA,Canada
GB,United Kingdom

Solution

Add an optional header parameter to seed config

Checklist

• I have read the contributing guide and understand what's expected of me.
• I have run this code in development, and it appears to resolve the stated issue.
• This PR includes tests, or tests are not required or relevant for this PR.
• This PR has no interface changes (e.g., macros, CLI, logs, JSON artifacts, config files, adapter interface, etc.) or this PR has already received feedback and approval from Product or DX.
• This PR includes type annotations for new and modified functions.

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[github-actions]

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[aammett]

Related PR dbt-labs/dbt-common#340 to modify the seed's agate helper function 🙂